Otho fulton



Feb. 14, 1933. o. FULTON 1,897,796

ELECTRICAL TRANSMISSION OF PICTURES Filed Oct. 5, 1928 /N VE/VTOR Ofho F on med Feb. 14, 1933 UNITED STATES PATENT OFFICE murmur. rmsmsmn or rrc'runns Application fled fletober 8, 1928, Serial No. 810,002, and in Austria October 13, 1987.

For transmitting a picture or a drawing or the like to a distance, it is necessary to decom ose the whole picture surface into points or ements and in some way or other to imli press upon a train of waves being transmitted the tone value of each point or element of the picture in succession. This 'may'be done in either of two ways. Either a signal of varying intensity, or a series of current impulses of uniform intensity but varying duration may be transmitted. It is with the latter method that the present invention is concerned.

The invention is particularly, though not exclusively, applicable to a system inwhich current impulses corresponding to the' picture elements are used to modulate a carrier wave of audio-frequency and this modulated wave of audio-frequency is utilized in its turn to modulate a carrier-wave of radio-fre uency. Where the current impulses correspon ing to the tone values of the several elements of the picture are used to modulate an alternating current, the frequency of the latter must'be very hi h compared with that of the impulses ii the tone values are to be correctly reproduced. .This is especially so in the case of half-tone pictures in which the transmitting ap aratus comprises a conducting foil upon w ich the picture is represented by lines of insulating material. In this case the current will in the ordinary way have a very sudden rise and fall.

More particularly in the case of high pic ture frequencies, considerable difliculties ocour in the amplification on account of the inductive resistances and capacity values which are particularly troublesome. Faults occur such as omission of half tones, subsequent action after the si al impulses, which faults, in the case of hal -tone pictures may lead to complete wiping out in the case of line drawings or the like, to the appearance of double outlines or even of white spaces along the 45 lines.

By means of the invention, the amplification absolutely necessary for the ractical transmission of pictures and modu ation of the transmitter or the like can be obtained even at the highest picture frequencies used.

The completely correct reproduction of short impulses of voltage or current is exceedingly difiicult since capacities and inductances exercise a very great influence and must be taken into account in building any amplifier arrangement. Indeed, in the case of currents with a very square wave form it is impossible to construct, in such a way as to avoid distortion, the various devices through which the picture currents have to pass before being radiated from the trans mitter. In addition, it is desirable to avoid the necessity for apparatus at the receiving end designed specially to deal with impulses of square wave form.

According to the present invention, a system for the transmission of pictures and other transmissions, in which the tone values of picture elements are represented by current impulses having a sudden rise and fall, is provided with means for retarding the rate of change of said impulses.

Such a system preferably comprises a source of current (such as a battery) electrically connected in series with a picture exploring means, a resistance, and a further resistance shunted by a condenser, for the purpose of producing, across the condenser, impulses of volta e whose rise and fall is comparatively gra ual.

The picture exploring means will in this case consist of some means of exploring successively the points or elements of the picture constituting a device the electrical properties of which change suddenly as the picture is transmitted. It may for instance comprise a rotating drum of conducting material upon which is stretched a copper foil upon which the picture is represented by lines of insulating material of varying width corresponding to the tone values of the picture elements and a conducting stylus which slowly traverses the drum lengthwise. It will be relized that as the drum rotates. the electrical resistance to a current flowing between the stylus and the drum changes almost instantaneously.

Such current impulses (converted, for example, into gradual voltage changes as de scribed) may be caused to modulate a carrier-wave so that the building up and dyin away of such modulated carrier-wave tal ies place com aratively gradually.

Means is pre erably provided for varying at will the characterictics of the gradual rise and fall of voltage or current, whether direct or alternating, so as to vary the character of the picture received. Thus, it is possible to adjust the values of capacity, resistance or inductance in the circuit so that in the case of short current impulses the maximum current value is never reached.

The result is that the gradation of the tone values of the pictures received can be arranged in the most favorable manner for each individual case. For instance, pictures otherwise unsuitable for transmission, that is to say, extremely hard or extremely soft, can be received at the receiving end with correct tone reproduction. This variability at will of the tone reproduction of pictures is a. desirable by-efiect, the chief advantage, however, is the possibility given for the first time by the arrangement mentioned, of ensuring the passage, without disturbance, of picture currents in the ordinary way, without any special arrangements at the transmitting or at the receiving end.

The current impulses conveniently be caused to produce comparatively gradual corresponding changes 0 the potential of a grid of a mixing valve, to the anode circuit of which is supplied an auxiliary carrierwave of audio-frequency, and from the anode circuit of which it is taken after modulation.

The control of the auxiliary frequency utilized as the carrier for the picture frequency, by the direct current impulse controlled in accordance with the above process, takes place in a mixing valve connection. These direct current impulses are supplied to the controlling electrode or electrodes of the three or more electrode valve used as the mixing valve, and the auxiliary frequency to be controlled and that already cancelled, is supplied to, or taken from, circuits which are connected to the other electrodes of the mixing valve.

A construction in connection with a simple feeler device is shown in the drawing, the picture being decomposed for instance into conducting and non-conducting screen lines.

The auxiliary frequency used is brought through the transformer T1 into the anode circuit of the mixing valve. If the feeler means pencil is at A on an insulating screen line, the battery B2 will produce through the resistance R2 such a negative voltage that the alternating voltage existing between the anode and cathode, will be compensated. If the contact is closed at A, the battery B1 will generate through the resistance R1 in the resistance R2 such a voltage of opposite potential that it will be possibel to take through the transformer T2 from the anode circuit an alternating voltage of the auxiliary frequency used, which can be further utilized for instance for the modulation of a wireless transmitter. When the contact in A is opened or closed, the above mentioned changes of voltage of the control electrode of the mixing valve will not take place instantaneously, but in accordance with the charging or discharge curve of the condenser C which can be controlled at will by the resistatncts R1 and R2 and the value of the capac- 1 y The nature and scope of the invention having been thus indicated and its preferred embodiment having been specifically described, what is claimed as new is:

1. In a system for the transmisison of ictures or ot er representations, the combination of a transmitting circuit comprisin a picture exploring means and a source of cictric current connected in series therewith for producing current impulses having a sudden rise and fall and representing the tone values of the picture, and a condenser also electrically connected in said circuit so as to reduce the rate of change of said impulses.

2. In a system for the transmisison of pietures or other representations, the combination of a transmitting circuit comprisin a picture exploring means and a source of e ectric current connected in series therewith for producin current impulses having a sudden rise and all and representing the tone values of the picture, and a condenser also connected in said circuit for reducing the abruptness of said impulses and a resistance in series with the condenser.

3. In a system for the transmission of ictures or 0t er representations, the comb1nation of a transmitting circuit comprisin a picture exploring means and a source of eFectic current connected in series therewith for producing current impulses having a sudden rise and fall and representing the tone values of the icture, and a condenser also connected in said circuit, a resistance in series with said condenser and with said exploring means and a further resistance in parallel with the said condenser.

4. In a system for the transmission of pietures or other representations, the combination of a transmitting circuit comprisin a picture exploring means and a source of e ectric current connected in series therewith for producing current impulses having a sudden put circuit.

OTHO FULTON.

CERTIFICATE OF CORRECTION.

Patent No. 1,897,796.

OTHO FULTON February 14, 1933.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 39. before cenvemently" insert the word "may"; same page. strike out claimsl to 3, comprising. lines 92 to 124; and line 125, strike out claim numeral "4."; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of April, A. l). 1933.

(Seal) rise and fall and representing the tone values of the picture, and a condenser also con in said circuit, a resistance in series with said condenser and with said exploring means 5 and a further resistance in parallel with the said condenser, and a thermionic valve having its input side connected across the said condenser, means for introducing a carrier wave into a circuit containing the output side of the thermionic valve and means for drawing the modulated energy from the said output circuit.

OTHO FULTON.

CERTIFICATE OF CORRECTION.

Patent No. 1,897,796. February 14, 1933.

OTHO FULTON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 39. before cenvemently" insert the word "may"; same page. strike out claimsl to 3, comprising. lines 92 to 124; and line 125, strike out claim numeral "4."; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of April, A. l). 1933.

M. J. Moore. 

